Citrullination, a posttranslational modification (PTM), has recently received significant interest in biomedicine, in particular autoimmune diseases. Cintrullination is the modification of peptidyl arginine to peptidyl citrulline catalyzed by peptidylarginine deiminases (PADs). The citrulline modification can dramatically change the structure and functions of proteins. Citrullination has been implicated in several physiological and pathological processes, including rheumatoid arthritis, multiple sclerosis, and Alzheimer?s disease. Thus, a small change in the protein, such as citrullination, can have great consequences for some inflammatory diseases. To date five different human PAD enzymes have been identified, however, cellular distributions and their specific roles are still not clear. At the present there are only a few citrullinated proteins known in mammalian cells. It is currently unknown if citrullination plays any potential role in the assembly or activation of the inflammasome, a multi- protein complex required for active IL-1b release, a powerful proinflammatory cytokine. In preliminary studies we have made a seminal discovery that citrullination plays a critical regulatory role in inflammasome activity and IL-1b release. Based on this knowledge we have now generated compelling preliminary data suggesting a key role of protein citrullination in a Kawasaki Disease (KD) vasculitis mouse model, which we have already established to be an IL-1b-driven cardiovascular disease model. Inhibition of PAD enzymes can block the LCWE-induced KD vasculitis model. This observation is highly novel and potentially of high impact not only for this vasculitis model but also for several other inflammatory diseases where an overactive NLRP3 inflammasome and IL-1b driven pathology is prominent. Based on these preliminary data we propose to investigate the mechanisms of these novel discoveries with the CENTRAL HYPOTHESIS that Peptidyl Arginine Deiminase-mediated citrullination is required for the inflammasome activation and IL-1b secretion, and that pathway is also crucial for LCWE-induced mouse vasculitis, coronary arteritis in this KD mouse model. Peptidyl arginine deiminase 4 is also a key component for neutrophil extracellular trap (NET) in neutrophils, however, the role of PAD in vasculitis was independent of its effect on neutrophils. Based on our preliminary data we hypothesize that PAD and citrullination play a crucial role in inflammasome activation in macrophages, and PAD inhibition thereby may treat the IL-1b driven cardiovascular pathologies that are associated with the KD vasculitis and myocarditis. To investigate these central hypotheses, we propose the following two specific aims: 1) Investigate the role of Peptidyl Arginine Deiminase and Protein Citrullination in inflammasome activation and vasculitis. 2) To determine the role of Peptidyl Arginine Deiminase during LCWE-induced KD vasculitis, coronary arteritis and AAA.